1. Field of the Invention
The present invention relates to a base station transmitting apparatus of a CDMA system, and more particularly, to an apparatus for detecting and adjusting a transmission power of a base station transmitter.
2. Description of the Background Art
FIG. 1 is a schematic block diagram of a transmitting power detecting apparatus of a CDMA system in accordance with a conventional art.
As shown in FIG. 1, a transmission power detecting apparatus of a conventional CDMA system includes a base station transmitting unit 100 for converting a PCM signal to a radio frequency (RF) CDMA signal and transmitting it to a terminal; a transmission power detecting unit 101 for detecting power of the RF CDMA signal transmitted from the base station transmitting unit 100; and a digital processor 102 for compensating the power of the RF signal detected by the transmission power detecting unit 101 for the loss caused by the temperature.
The base station transmitting unit 100 includes a modem 10 for directly spreading a spectrum of a PCM data; a digital combiner 20 for summing the directly spread spectrum of the CDMA signal by channels (I, Q); an IF signal processor 30 for converting a base band CDMA signal outputted from the digital combiner 20 to an intermediate frequency (IF) signal; and an RF signal processor 40 for converting/amplifying the converted IF CDMA signal to a radio frequency (RF) signal and outputting it to an antenna.
The modem 10 includes a Walsh generator 11 for multiplying the inputted CDMA signal by a Walsh code; and first and second multipliers 12 and 13 for respectively multiplying pseudo noise (PN-I and PN-Q) codes to the output signal of the Walsh generator 11 in order to directly spread the spectrum of the CDMA signal.
The combiner 20 includes adders 21 and 22 for adding the CDMA signal which has been directly spread in the modem 10 by sectors.
The IF signal processor 30 includes finite impulse response filters (FIR) 31 and 32 for respectively filtering the digital CDMA signal outputted from the combiner 20; digital/analog converters (DAC) 33 and 34 for converting the filtered digital CDMA signal to an analog signal; low pass filters (LPF) 35 and 36 for filtering the analog-converted CDMA signal; mixers 37 and 38 for multiplying the filtered analog CDMA signal by a carrier signal (cosωt, sinωt) and converting it into an IF CDMA signal; and an adder 39 for adding the analog CDMA signals which have been converted into the IF signals by the mixers 37 and 38 and quadrature phase-shift key (QPSK) modulating it.
The RF signal processor 40 includes a mixer 41 for mixing the IF CDMA signal which has been QPSK modulated by the IF signal processor 30 with a local oscillation signal (LORF) and up-converting it to an RF CDMA signal; a band pass filter (BPF) 42 for removing a spurious component of the RF CDMA signal outputted from the mixer 41; and an amplifier 43 for amplifying the RF CDMA signal which has been filtered by the BPF 42 and outputting it to the antenna.
The transmission power detecting unit 101 includes a mixer 51 for mixing the RF CDMA signal with a local oscillation signal (LOIF) and down-converting it to an IF CDMA signal; a BPF 52 for filtering the IF CDMA signal; a received signal strength indicator (RSSI) detector 53 for detecting a power strength of the IF CDMA signal which has been filtered by the BPF 52; and an analog/digital converter (ADC) 54 for digital-converting the voltage value detected by the RSSI detector 53.
Reference numerals 103 and 104 denote a temperature sensor and a memory, respectively.
The operation of the transmission power adjusting unit of the base station transmitting apparatus according to the conventional art constructed as described above will now be explained with reference to the accompanying drawings.
When the PCM data is inputted, the base station modem 10 directly spread the spectrum of the PCM data to the digital baseband CDMA signal by sectors, and outputs it through the channel ‘I’ (Inphase) and a channel ‘Q’ (Quadrature phase) to the digital combiner 20.
Then, the digital combiner 20 sums the CDMA signals outputted from the base station modem 10 by means of the multipliers 21 and 22 by sectors, and outputs it to the IF processor 30.
The IF processor 30 converts the digital CDMA signal outputted from the digital combiner 20 into an IF CDMA signal and sums the IF CDMA signals of the channel ‘I’ and the channel ‘Q’ and QPSK-modulates it. That is, the FIR filters 31 and 32 of the IF processor 13 filter the digital baseband CDMA signal inputted through the channel ‘I’ and the channel ‘Q’, respectively, and the DACs 33 and 34 convert the filtered digital CDMA signal into an analog CDMA signal.
LPFs 35 and 36 removes an unnecessary components from the analog-converted CDMA signal and output it to the mixers 37 and 38. The mixers 37 and 38 mix the filtered analog CDMA signals with the carrier signal (cosωt, sinωt) and convert the baseband CDMA signal into an IF CDMA signal, respectively.
Then, the adder 39 adds the analog IF CDMA signals outputted from the mixers 37 and 38 and outputs QPSK-modulated CDMA signals.
The mixer 41 of the RF signal processor 40 mixes the local oscillation signal (LORF) with the QPSK-modulated CDMA signal and converts the analog IF CDMA signal into an analog RF CDMA signal.
The BPF 42 removes a spurious component from the RF CDMA signal and transmits through the amplifier 43. Accordingly, the amplifier 43 amplifies the RF CDMA signal and transmits it through the antenna to a destination.
At this time, the transmission power detector 101 detects the power of the RF CDMA signal outputted from the base station transmitting unit 100 in the voltage form and outputs it to the digital processor 102. That is, the mixer 51 mixes the RF CDMA signal outputted from the base station transmitting unit 100 and the local oscillation signal (LOIF) and converts it into an IF CDMA signal. The converted IF CDMA signal is filtered by the BPF 52 and inputted to the RSSI detector 53.
The RSSI detector 53 outputs a certain voltage corresponding to the strength of the inputted IF CDMA signal to the ADC 54, and the ADC 54 digitally converts the inputted analog voltage and outputs it to the digital processor 102.
Accordingly, the digital processor 102 reads a compensation value stored in the memory 104 corresponding to a current temperature provided from the temperature sensor 103, and performs a compensation operation for the digital voltage inputted from the ADC 54. That is, the digital processor 102 recognizes the power of the RF CDMA signal currently outputted from the base station transmitting unit 100 by adjusting the strength of the RF CDMA signal according to the temperature.
In this manner, the transmission power adjusting unit of the conventional base station transmitting apparatus detects the power of the final RF CDMA signal detected by the RSSI detector and compensates the power of the RF CDMA signal according to the temperature change.
In this respect, since the thermostatic device such as the RSSI detector 53 is generally sensitive to heat, failing to accurately detect the power of the detected RF CDMA signal.
Especially, as shown in FIG. 2, the analog voltage outputted from the RSSI detector 53 exhibits the sharp change (Δt1→Δt3) in the time domain, having a high possibility that an error would occur in measuring the power.
In addition, since the data stored in the memory 104 has been produced on the basis of an overhead channel, that is, for example, a pilot channel, a sync channel and a paging channel, etc. except for a traffic, when the power of the RF CDMA signal is actually determined on the basis of the stored data, a considerable error occurs inevitably.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.